[Qemu-devel] [PATCH v3 0/1] migration: calculate expected_downtime with ram_bytes_remaining()

[Balamuruhan S <bala24@linux.vnet.ibm.com>]

V3:

* commit message to be updated with the changes done by the patch since
v1, review comment by David Gibson.

* Included Michael Roth as ``Reported-by:`` for bringing up the concern.

v2:

There is some difference in expected_downtime value due to following
reason,

1. bandwidth and expected_downtime value are calculated in
migration_update_counters() during each iteration from
migration_thread()

2. remaining ram is calculated in qmp_query_migrate() when we actually
call "info migrate"

This v2 patch where bandwidth, expected_downtime and remaining ram are
calculated in migration_update_counters(), retrieve the same value
during
"info migrate". By this approach we get almost close enough value,

(qemu) info migrate
globals:
store-global-state: on
only-migratable: off
send-configuration: on
send-section-footer: on
capabilities: xbzrle: off rdma-pin-all: off auto-converge: off
zero-blocks: off compress: off events: off postcopy-ram: off x-colo: off
release-ram: off block: off return-path: off pause-before-switchover:
off x-multifd: off dirty-bitmaps: off
Migration status: active
total time: 319737 milliseconds
expected downtime: 1054 milliseconds
setup: 16 milliseconds
transferred ram: 3669862 kbytes
throughput: 108.92 mbps
remaining ram: 14016 kbytes
total ram: 8388864 kbytes
duplicate: 2296276 pages
skipped: 0 pages
normal: 910639 pages
normal bytes: 3642556 kbytes
dirty sync count: 249
page size: 4 kbytes
dirty pages rate: 4626 pages

Calculation:
calculated value = (14016 * 8 ) / 108.92 = 1029.452809401 milliseconds
actual value = 1054 milliseconds

since v1:
use ram_bytes_remaining() instead of dirty_pages_rate * page_size to
calculate expected_downtime to be more accurate.

Regards,
Bala

Balamuruhan S (1):
  migration: calculate expected_downtime with ram_bytes_remaining()

 migration/migration.c | 11 ++++++++---
 migration/migration.h |  1 +
 2 files changed, 9 insertions(+), 3 deletions(-)

-- 
2.14.3